In cellular systems, when a mobile user equipment (UE) moves from one cell to another, it performs cell selection/reselection and handover operations. Also, the UE performs radio resource management (RRM) measurements of the reference signal quality transmitted by the neighboring cells. In current long-term evolution (LTE) systems, a UE reports two parameters using reference signals: reference signal received power (RSRP) and reference signal received quality (RSRQ).
RSRP provides information about signal power from a specific cell while excluding noise and interference from other cells. It is defined as the average power of Resource Elements (RE) that carry cell specific reference signals (RS) over the entire bandwidth, i.e. RSRP is only measured in the symbols carrying the RS. For RSRP, the UE measures the power of multiple resource elements used to transmit the reference signal and takes their average. RSRQ (Reference Signal Received Quality) provides the link quality considering also RSSI (Received Signal Strength Indicator) and the number of used Resource Blocks (N). RSRQ is indicative of the quality of the received reference signal including the contribution of interference.
Conventional RRM measurements convey power information of the target and interfering cells. However, it is not sufficient to accurately judge the link quality for more advanced receiver structures with multiple receive antennas, particularly for inter-frequency handovers. The existing measurements based on RSRP would not be sufficient for reliable handover decision, since the MIMO dimension is lost in the current measurements.